Vending machines of all types have become commonplace in today's societies. One of the more recent types of vending machines are those which dispense refrigerated, frozen or semi-frozen items. The refrigeration units of such vending machines are required to maintain the temperature of the refrigerated portion(s) of the vending machine at various temperatures depending upon the nature of the products being dispensed. For example canned or bottled beverages or cooled foods are typically maintained at temperatures of about 36.degree. to 45.degree. F. Semifrozen goods such as ice-cream are maintained at a temperature of about 9.degree. F.; whereas frozen goods require refrigeration temperatures below -5.degree. F. At such lower temperatures, condensation and eventually ice has a tendency to rapidly form on the evaporator coils of the machine's refrigeration unit, requiring frequent, routine defrosting of the evaporator coils. It is important to minimize the defrosting cycle time and to maintain the temperature of the refrigerated compartments during the defrosting cycle to prevent thawing or spoiling of the items stored therein. The refrigerated chamber(s) gain temperature during a defrosting cycle through normal heat gain through the chamber walls, through leakage through any seals associated with the chamber(s) and through any vending activities during the defrosting cycle. Further, the mechanics of the defrosting operation itself have been one of the largest contributors of heat gain to the refrigerated compartment(s) during a defrosting cycle.
The defrosting operation is typically accomplished by applying heat to the iced evaporator coils. In prior art refrigeration configurations, a significant amount of the applied defrosting heat has escaped through the airflow ducts associated with the evaporator coils, from the refrigeration unit and into the refrigerated compartment. Such escaping heat not only increases the defrosting time by requiring the application of yet more heat to the evaporator coils, but also directly increases the ambient air temperature of the refrigerated compartment(s). With prior art defrosting systems, the temperature within a refrigerated compartment housing frozen food could rise as high as an unacceptable 40.degree. F. during a defrosting cycle and for a beverage or food containing compartment, as high as 60.degree. to 70.degree. F. The present invention addresses the above-described shortcomings and problems associated with the defrosting of prior art refrigerated vending machines.